A Harvard university team finds compared to placebo, neither vitamin D or omega-3 Fatty Acids (FA) were linked to improvement in knee symptoms in older adults with chronic daily knee pain and self-reported knee OA.
“Our trial adds to this body of evidence through the use of a large racially-diverse population-based cohort with over four years of follow-up,” says the team, led by Dr Lindsey MacFarlane, instructor in medicine at Brigham and Women's hospital based in Boston, Massachusetts.
“Our findings further support that vitamin D supplementation doses do not have a role in the reduction of knee pain in patients with OA even among the subgroup with low vitamin D.”
Recent interest has focused on the role of vitamin D in OA due to vitamin D’s function in bone resorption and muscle strength, as well as its anti-inflammatory properties.
Marine omega-3 fatty acids found in fish oils, have also been touted for their ability to mitigate inflammation and the catabolic environment that promotes cartilage degradation.
While studies show a link with lower vitamin D levels to pain and OA progression, several randomised controlled trials (RCT) of vitamin D supplementation in OA yield conflicting results.
Fewer RCTs have been carried out using fish oil, although one notable paper conducted a two-year RCT of low versus high-dose fish oil on patients with symptomatic knee OA.
Here the team showed that participants on low-dose fish oil had statistically significantly lower pain scores at 18 and 24 months compared to the high-dose group. However, no placebo group was analysed.
Study details
In this latest analysis, the team took results from a patient subgroup enrolled in the VITamin D and OmegA-3 TriaL (VITAL), a nationwide trial with five years of randomised intervention in the primary prevention of cancer and cardiovascular disease.
Here, almost 1400 individuals were randomised to supplement with vitamin D3 (cholecalciferol; 2000 IU/day), marine omega-3 fatty acids (Omacor 1g/d, 840 mg eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in a 1.3 to 1 ratio), or placebo and followed for 5.3 years.
The group completed a pain and stiffness test that looked at the impact pain had on completing activities including walking and climbing stairs.
Results revealed that pain scores did not differ between vitamin D or omega-3 FA and placebo at any time point during follow-up. No change in analgesic use was noted between the two groups over the study period.
“Over the mean of 5.3 years of follow-up, a small decrease in reported knee pain was observed, but this occurred in both the treatment and placebo groups and may reflect regression to the mean and some loss of participants to total knee replacement (TKR),” the team says.
“At no time point did pain scores statistically differ between treatment and placebo, and treatment arm did not significantly affect pain scores over time.
“No clinically or statistically significant reductions in WOMAC Function or Stiffness were identified in either treatment group compared to placebo.”
Conflicting evidence
The team points to prior conflicting RCTs looking at vitamin D efficacy on knee pain in OA. In a two-year trial of participants with symptomatic knee OA and low vitamin D (12.5 nmol/L to 60nmol/L) randomised to vitamin D versus placebo, there were no significant changes in WOMAC pain scores between the treatment groups.
However, post hoc analysis revealed significant improvements in the vitamin D group for total WOMAC score and WOMAC function as well as a greater proportion of OMERACT-OARSI responders.
In a one-year pilot trial of subjects with symptomatic knee OA and vitamin D insufficiency randomised to vitamin D versus placebo the study reported significant improvement in Pain and Function scores in the vitamin D group
However, these differences did not meet the threshold for minimal clinically improved difference.
Source: Arthritis Rheumatol
Published online: doi.org/10.1002/art.41416
“The effects of Vitamin D and Marine Omega-3 fatty acid supplementation on chronic knee pain in older US adults: results from a randomised trial.”
Authors: Iversen MD, Katz JN, Costenbader KH.